Nano- and microparticles can interact with living cells and tissues on a wide range of length scales and offer versatile applications in medicine. From a chemical point of view, the challenge is to synthesize and control their properties in such a way that they can be used in vivo including the option for clinical translation while addressing a certain medical need. Especially interesting are nanoparticles as contrast agents in combination with e.g. MRI and CT imaging but also for drug delivery. For the latter, we investigate stimuli-responsive particles for drug delivery that release locally their payload when exposed to e.g. ultrasound providing a pressure or temperature stimulus. One example are microcapsules filled with a perfluorinated oil which can be visualized with 19-F-MRI while drug release can be induced with ultrasound pressure pulses.  Another example are temperature sensitive liposomes (TSLs) that can be loaded with a drug. At body temperature, these TSLs stably encapsulate the drug but release their payload in a tumor tissue once it is heated to hyperthermic temperatures using MR-HIFU